Wireless communication systems commonly include information carrying modulated carrier signals that are wirelessly transmitted from a transmission source to one or more receivers within an area or region.
Wireless communication systems serving stationary and mobile wireless subscribers are rapidly gaining popularity, resulting in a need for greater efficiency in the use of the available radio frequency spectrum. This goal is complicated because wireless communications channels between transmit and receive devices are inherently variable, so the characteristics of wireless channels, such as signal quality, generally vary in time, frequency and space. Under good conditions wireless channels exhibit good communication parameters, e.g., large data capacity, high signal quality, high spectral efficiency and throughput. However, under poor channel conditions, these parameters have significantly lower values. For example, when the wireless channel is degraded the transmitted data may experience excessive corruption, manifesting as high bit-error rates or packet error rates. The degradation of the channel can be due to a multitude of factors such as general noise in the channel, multipath fading, loss of line-of-sight path, excessive Co-Channel Interference (CCI) and other factors.
Motivated by these complications, prior art wireless systems have employed adaptive modulation of the transmitted signals with the use of feedback from the receiver as well as adaptive coding and receiver feedback to adjust data transmission to changing channel conditions. Such adaptive modulation has been applied to Single Input Single Output (SISO) as well as to Multiple Input Multiple Output (MIMO) systems, e.g., systems with antenna arrays at both the transmit and receive ends.
In wireless systems (mobile and fixed), signal degradation and corruption is primarily due to interference from other cellular users within or near a given cell and multipath fading, in which the received amplitude and phase of a signal varies over time. In Fixed Wireless Access (FWA) systems, that is, where the receiver remains stationary, signal fading rate is less than in mobile systems. In this case, the channel coherence time or the time during which the channel estimate remains stable is longer since the receiver does not move.
Prior art wireless systems have employed adaptive modulation of the transmitted signals with the use of feedback from the receiver as well as adaptive coding and receiver feedback to adapt data transmission to changing channel conditions. Such adaptive modulation is applied to Single Input Single Output (SISO) systems. In both SISO and MIMO systems, however, the fundamental problem of efficient choice of the mode to be applied to the transmitted data remains.
It would be an advance to provide a mode selection technique which allows the system to rapidly and efficiently select the appropriate mode for encoding data in a quickly changing channel. It is important that such technique be efficient in all wireless systems, including Multiple Input Multiple Output (MIMO), Multiple Input Single Output (MISO), Single Input Single Output (SISO) and Single Input Multiple Output (SIMO) systems as well as systems using multiple carrier frequencies, for example, OFDM systems.